1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine which controls an amount of power generated by an electric generator mounted in the internal combustion engine, and in particular to such a control apparatus which allows a secure purging of vaporized gas from a fuel tank together with a suppression of fluctuation in rotation of the internal combustion engine.
2. Description of the Related Art
An internal combustion engine incorporates a vaporized fuel treatment unit which serves to treat the vaporized fuel generated in a fuel tank without emitting the vaporized fuel into the atmosphere. The vaporized fuel treatment unit includes a canister to collect the vaporized fuel from the fuel tank. The vaporized fuel is temporarily absorbed by an absorbent in the canister, and during the operation of the internal combustion engine, the vaporized fuel treatment unit purges a fuel ingredient, hydrocarbon (HC) for example, in the vaporized fuel collected in the canister through a purge path to an intake path for treatment, utilizing a negative pressure produced in the intake path.
A control apparatus for the internal combustion engine decreases an amount of fuel injection in accordance with a vapor concentration of the vaporized fuel from the fuel tank when the vapor concentration is high. In an idling operation state of the internal combustion engine, however, such a control makes an actual amount of fuel injection excessively low since the amount of fuel injection is low in the idling operation state because of a low pressure even without the controlled decrease of fuel injection in accordance with the amount to be treated. When the amount of fuel injection is excessively low, stability of combustion is negatively affected to lower efficiency of emission purification or to functionally disable an injection by a fuel injector. Hence, a minimum amount of fuel injection (minimum injection time period) is generally set, and the control apparatus controls the actual injection amount to be the set minimum amount and decreases the treated amount of vaporized fuel when the amount of fuel injection drops below the minimum amount of fuel injection.
When features such as reduction in friction loss, enhancement of combustion in the idling operation state, and reduction of the number of rotations in idling, are to be realized for the reduction of fuel consumption of the internal combustion engine, an amount of required air in the idling operation state decreases thereby lowering a reference fuel injection amount, and the reference fuel injection amount approaches the above described minimum fuel injection amount to lessen the margin. Thus in the idling operation state, because of the small margin of the fuel injection amount, the vaporized fuel treatment unit cannot properly perform the purging treatment of a predetermined amount of vaporized fuel collected in the canister.
A technique is proposed to solve such a problem in Japanese Patent Laid-Open No. 2002-013446, for example. According to the disclosed technique, when the amount of vaporized fuel from the fuel tank is high in the idling operation state, the number of rotations is set to a higher value than usual in order to increase the amount of air intake and therefore the amount to be purged.
The internal combustion engine incorporates an alternator as an electric generator for operations such as a battery charging and a power supply to various electric parts. The alternator is drivably connected to a crank shaft of the internal combustion engine via a belt or the like and is driven to rotate and generates power by the operation of the internal combustion engine. The amount of power generated by the alternator is controlled by the control apparatus so that the charging voltage varies according to the operation states of the internal combustion engine, i.e., normal vehicle running, acceleration running, and deceleration running, the state of use of various electric parts, or the like.
Since various parameters are likely to fluctuate in the idling operation state of the internal combustion engine, a fluctuation in the rotation occurs, though minute. In addition, since the amount of power generation (charging voltage) of the alternator is changed according to the operation state of the internal combustion engine, the amount of power generation also fluctuates in a low rotation range, e.g. in the idling. The fluctuations in rotation and the amount of power generation function as power generation friction of the alternator, and a generated torque in the internal combustion engine is an approximate value of the sum of the friction of the internal combustion engine and the power generation friction of the alternator. Hence, when the power generation friction of the alternator varies, the generated torque in the internal combustion engine, therefore, the amount of air intake and the amount of fuel injection fluctuate to cause the fluctuation in rotation of the internal combustion engine, thereby deteriorating the drivability.
When the amount of air intake and the amount of fuel injection vary in the idling operation state of the internal combustion engine, the vaporized fuel treatment unit cannot properly purge the vaporized fuel collected in the canister to the intake path thereby preventing the secure treatment of the vaporized fuel.